I know this has been covered many times, and thought I could do this ,but...

I have an older laptop that was running Windows 7 very slowly. I emptied a lot of stuff off before I did a factory reinstall. Following many tutorials I moved my itunes folder to a new flash drive successfully. I checked before I did the reboot, and itunes (with itunes programme still on the laptop) was playing my music from the flash drive OK. At that point I did a factory reset of the laptop, and started again with Windows 7. Downloaded the latest browser, got my email account up & running etc.I then downloaded the latest itunes to the laptop (12.5.5).
Next, as described in many tutorials I connected the flash drive and and went the edit/preferences/advanced route. I pressed the change button and browse till i found the flash drive and the folder i had created called itunes with my files on. I selected that folder, then pressed OK at the bottom....but nothing happens ? Should this not work ?. I really do not want to fill up the laptop with all my 14gb of music. Should I maybe have downloaded the itunes programme to the flash drive as well ?. What is the reset button in that change section mentioned earlier...do I need to use this ?. A full step by step guide would be much appreciated as I am of an older generation, and did not grow up with computers.